Process for making concrete and cement mortar



Patented Apr. 19 1932' "UNITED STATES PATENT OFFICE.

BOY CROSS, OF KANSAS CITY, MISSOURI, ASSIGNOR TO SILICA PRODUCTS (JO- OF KANSAS CITY, MISSOURI, A CORPORATION OF DELAWARE PROCESS FOR MAKING CONCRETE AND CEMENT MORTAR No Drawing.

This is an improvement in rocesses f making concrete and mortar. t is appl edto all types of hydraulic cement, but particularly to what is known as Portland cement.

5 Heretofore, it has been the general practice It has been the general belief that if concrete is mixed with water it must be placed at the earliest possible moment to get the best results. It has been generally supposed that if this concrete is laced over a longer period than 30 minutes, it would be highly inferior and that if it were placed after the normal time for the initial set of the cement as determined by the usual means, the concrete would be ruined. This process is therefore the outcome of the discovery that Portlan tically all instances, there is a great improvementin the concrete or mortar.

As an illustration of this fact, a 1:2:4': mixture of concrete, in other words, concrete containing one part of cement, two parts of 0 sand and four arts of crushed rock by volume and using .5 allons of water per cubic foot of cement, s owed a strength after hardening for 28 vdays, of from 2,500 pounds to 4,200 pounds per square inch in terms com ression strength, the lower strength being obtained after two minutes mixing and the higher strength after seven hours of mixing. Intermediate strengths gradually increasing from two minutes up to seven'hours 40 were obtained and decreasing again after the seven hour period. After 24 hours of mixing, the concrete still gave a strength greatcement itself, or other calcium sihcate' mag er than the strength after two minutes mixing. It is obviously impracticable to continuously mix the sand, rock. water andce- 'Many factors enter into the Application fled July 2, 1926. serial no. 289,676.

ment for a period .of seven hours howeverf I and since-the value of the longer period 0 exposure depends upon the action upon the Portland cement itself, the Portland cement is therefore subjected alone to the action of water and the same results in a general way were obtained. If the cement 1s hydrated to form a slurry and is then added to the aggregate, it gives the usual time strength of cement or mortar. If the slurry is mixed, for exam le, in the ratio of one part of the cement w ich it contains, to three parts of sand, then again, the maximum strength with the same cement above referredto was greatest at a period of seven hours. It is obvious that the time at which the maximum strength is obtained will vary according to the particular type of Portland cement used. In the case of so-called quickly hardening cement, this time is considerably less; It is, also less in the case of finely ground cement. uestion as to exact strength. obtained at di erent periods, but in general, it is found that the hydration of the cement for a long period of time great- 1 increases the strength of the concrete made om it. In general, the prem'ixing' of the cement itself with water g1ves a superior result and a maximum strength at an earlier period than if all the materials were mixed simultaneously. Any period over five minutes shows a marked improvement. In, the case of many cements or in many mixtures, it 'is necessary to use so much water that ,the slurry is very thin and the cement articles tend to separate. In such cases, .w ich are quite common,- it is necessary or desirable to use a thickening agent. Among the thickenbe treated with acid for use as athick'bnin agent. Insome instances, Portland cement the thickening action of the Port and cement.

In a typical case, 5% by weight of sulphuric acid would be used. If bentonite is used, a

typical quantity would be 2% of the weight of the cement. Another benefit of premixmg the cement before adding the aggregate is the fact that the aggregate may be used in a drier condition than normally so that it will absorb part of the water from the slurry, causing a lower water-cement ratio next to the aggregate, thus increasing the strength of the concrete.

Instead of premixing the cement only, the concrete may also he premixed; or the sand and the cement alone may be mixed with the water. A typical and practical wa in such cases is to compound all of the ingre ients, including the cement, the sand, the rock, water, and any admixture that may be desired in the central mixing plant. T is may be then dumped into a truck of any type. This truck may be an ordinary truck, one s ecially made for hauling concrete, or one wit a screw con- 3. A process of increasing the strength of crete.

ROY CROSS.

veyor for mixing and unloading which is used in some localities. The cement may be left in the truck for a period up to six or seven hours. In an ordinary instance it would be in the truck for a eriod of not over one-half hour, as this woul be a typical time required for hauling it to the job where it is to be placed. When the concrete is dumped from the truck it is agitated enough to thoroughly break up any tendency for the concrete to become stiff; or, if the truck with the conveyor blades is used, the dum ing by means of these conveyor blades is su cient to thoroughly limber up the concrete. Of course if a satisfactory admixture is used to prevent segregation, t e mere dumping from the truck is often sufiicient. The same conditions also apply to the hauling of concrete more than ten or fifteen minutes after it has been premixed; but, particularly in connection with the use of admixtures such as elatinizing clay and diatomaceous earth, it 1s possible to remix the concrete after many hours. Concrete has actually been remixed in this process after a period of 24 hours without destroying more than 25% of its setting power.

I claim as my invention:

1. A process of making concrete or mortar which comprises remixing Portland cement, an inorganic thic ening agent and water for more than thirty minutes, and then intimately dispersing mineral aggregate into the premixture.

2. A process of making concrete or mortar which comprises premixing for a period of at least thirt minutes, Portland cement, bentonite an water and then intimately dispersing mmeral aggregate into the premlxture. 

